From the internal art and the unpublished document as of the foreign priority date of this application, DE 10 2012 101507 (now published on Aug. 29, 2013 as DE 10 2012 101507 A1 and Feb. 26, 2015 as US 20150053716 A1), it is known to measure the internal pressure in the container via suitable electric or mechanical sensors, for example on the container wall or also on the dispensing hose. If there is a drop below a certain pressure during the dispensing, the container is compressed again until the desired pressure is once again reached. It would also be possible to measure the pressure in the container or in the hose using a manometer (the measurement thus being carried out in contact with the product). The content of the disclosure of DE 10 2012 101 507, and in particular of the passages relating to the subjects of the dependent claims therein, is hereby also fully incorporated by way of reference into the subject matter of the present application.
In practice, however, this pressure measurement by means of sensors proves to be relatively difficult. In particular, pressure measurement by a test pin against the container wall would be relatively inaccurate and in particular also depends on the wall thickness of the container and the deformability of the container wall. Particularly in the case of plastic containers produced in a blow-moulding process, the wall thickness of the containers is not always uniform and may even fluctuate from container to container. The wall thickness also depends on the ambient conditions of a blow-moulding machine, and also on the plastic preforms used. An accurate measurement is therefore difficult or very complicated.
It is also known from the internal art of the applicant to measure the pressure within the container via a sleeve over the dispensing hose, in a manner similar to the procedure when measuring blood pressure. However, this method is also dependent on the hose material, that is to say in particular on the wall thickness, material and temperature thereof. Integrating in the hose a pressure sensor which makes contact with the product is also problematic when using disposable parts, for example disposable dispensing hoses. In this case, said sensor would have to be cleaned regularly.